The vascular endothelial cell is uniquely situated to play an active role in the transduction of pro-inflammatory signals from the interstitial tissues to circulating neutrophils. The goals of our principal projects are (i) to study the role of endothelial cytosolic calcium levels in alterations in vascular permeability in response to humoral inflammatory mediators, and (ii) to examine the role of the endothelial cell in transduction of chemoattractant signals from interstitial sites to circulating leukocytes. Using the fluorescent calcium indicator quin2, we have shown a rise in endothelial cytosolic calcium in response to the neutrophil independent promoters of vascular permeability (histamine and acetyl glyceryl ether phosphoryl choline (platelet activating factor)) whereas neutrophil dependent promoters of increased vascular permeability (C5a, formyl-methionyl-leucyl-phenylalanine, and LTB4) elicit no change in endothelial cytosolic calcium. We have characterized in detail the alterations in endothelial cytosolic calcium in response to histamine and correlated these with changes in endothelial shape and monolayer integrity monitored by macromolecular diffusion across cultured endothelial monolayers. Recent reports have demonstrated receptor mediated endocytosis and vectorial transport of intact insulin by cultured vascular endothelial cells. We have confirmed a prior observation that endothelial cells bind formyl peptide chemoattractants and are investigating the possibility that, in an analogous fashion, the endothelial cell directs transport of chemoattractant peptides from interstitial sites to the vascular lumen.